Combustion control system



July 16, 1968 5 U 1 ET AL 3,393,037

COMBUSTION CONTROL SYSTEM Filed Dec. 7, 1966 OPER.

CONT.

FIG I United States Patent 3,393,037 COMBUSTION CONTROL SYSTEM Philip Giuffrida, North Andover, and Phillip J. Cade,

Winchester, Mass., assignors to Electronics Corporation of America, Cambridge, Mass, a corporation of Massachusetts Filed Dec. 7, 1966, Ser. No. 599,885 22 Claims. (Cl. 43124) ABSTRACT OF THE DISCLOSURE A combustion control system directly energizes a blower in response to a request for heat in a pre-purge operation and the resulting air flow in the combustion chamber closes an air flow responsive switch to energize scanner electronics and capacitor timer apparatus. Energization of the timer apparatus is dependent on proper condition of a lockout actuator and a scanner controlled element. The timer incorporates a unijunction transistor which is biased to a nonconductive condition, which nonconductive condition is overcome through charging of a capacitor in an RC circuit. Upon completion of the time delay, the charge on the capacitor energizes a control relay, which is locked in to bypass the timer, and which initiates an ignition sequence. Any transient improper operation of the scanner electronics resets the timer and restarts the pre-purge timing interval.

Summary of invention This invention relates to electrical control circuitry and more particularly to control circuitry particularly adapted for use in combustion supervision systems.

In conjunction with the safe operation of a combustion system, it is desirable to provide a supervising system which programs a sequence of operations to initiate the desired combustion condition and then to supervise on a continuing basis that established combustion condition. In such an installation, it is desirable to ventilate the combustion chamber by forcing air through that chamber for a predetermined period prior to attempting to establish flame in the combustion chamber. Further it is desirable to check for the proper operation of the flame sensing components and to prevent the establishment of ignition if the flame sensor circuitry is operating improperly.

It is an object of this invention to provide novel and improved apparatus for use in the programming of fuel burners and the supervision of combustion conditions established by such fuel burners.

Another object of the invention is to provide novel and improved apparatus which reduces the complexity of fuel burner control.

Still another object of the invention is to provide novel and improved fuel burner control which is compact, economical and meets stringent requirements established by supervising agencies.

Still another object of the invention is to provide a novel and improved control system for sequencing a pre-purge ventilation of the combustion chamber and then a flame initiation sequence in a safe manner, coordinated with lock-out arrangements which terminate flame and the operation of the system in the event of improper operation.

In accordance with the invention there is provided control apparatus used with a fuel burner installation that includes a fuel control, a capacitor timer, a control relay, and an auxiliary device such as a blower which forces air through the combustion chamber. In response to a request for heat a capacitor timer is actuated and upon completion of its timing interval the charge on the capaciice tor is utilized to energize the control relay which initiates the desired combustion condition. The auxiliary device operates during the timing interval. For example, in a particular system, an operating control, in response to a request for heat, applies a signal directly to the blower to initiate air flow through the combustion chamber in a purging operation. In response to the resultant air flow, a flame scanner system and the capacitor timer are energized. Connected in series with the timer is an actuator of a lock-out device and a normally closed switch responsive to the flame scanner. Thus, if either the lock-out actuator or the flame scanner controlled switch is in improper condition, the timer is disabled. Provided the circuit components (blower, scanner and lock-out actuator) are operating properly, the timer, after a predetermined interval energizes a control relay which initiates a flame ignition sequence.

In the preferred embodiments, the timer includes a unijunction transistor having a timing network connected to its control electrode and a biasing potential applied to a second electrode from a DC source. The DC source also applies electric potential to the timing network to charge a capacitor in the timing network to impress on the control electrode of the unijunction transistor an increasing potential which, after a predetermined time, overcomes the bias on that device so that the transistor conducts and transfers the capacitor charge to energize the control relay. Upon energization of the control relay, a holding circuit is completed which bypasses the timer and maintains the control relay energized to supervise the ignition and flame cycles of the control system.

The invention thus provides a simple and compact, and yet extremely reliable fuel burner control system. Other objects, features and advantages of the invention will be seen as the following description of particular embodiments thereof progress, in conjunction with the drawings, in which:

FIG. 1 is a schematic diagram of a combustion control system constructed in accordance with the invention; and

FIG. 2 is a schematic diagram of a modified form of electronic timing interlock suitable for use in the system shown in FIG. 1.

Description of particular embodiments With reference to FIG. 1, control power is applied to the circuit at terminals 10, 12. Connected in series with terminal 10 is a limit switch 14 and an operating control 16 such as a thermostat. The system further includes an alarm unit 18, a blower motor 20, an ignition unit 22, a pilot fuel control 24 and a main fuel control 26. In addition, a switch 28 that is responsive to air flow produced by blower 20 which is connected in series between control 16 and the primary Winding 30 of transformer 32.

A first secondary winding 34 of transformer 32 is connected to and energizes electronic circuitry 36 which receives input from flame scanner unit 38 and in response to such an input provides an output signal which energizes flame relay 40.

A second secondary winding 42 of transformer 32 has a center tap 44 producing a twelve volt output and a terminal 46 which produces an 18 volt output.

Connected to terminal 46 is a lock-out heater element 48 which is in series with normally closed flame relay contact 404, diode 50 and capacitor 52. Connected to the upper terminal of capacitor 52 is resistor 54 which applies a biasing signal to electrode 56 of unijunction transistor 58. A second unijunction transistor electrode 60 is connected to the coil 62 of a control relay. The emitter 64 of transistor 58 is connected to an RC timing network that includes resistor 66 and capacitor 68. Connected across capacitor 68 is discharge contact 40-2 operated by flame relay 40. Connected to electrode 60 is a series circuit composed of holding contact 62-1 operated by coil 62 and resistor 70. A second contact 62-2, also operated by coil 62, is connected between center tap terminal 44 of transformer secondary 42 and flame relay contact 40-1.

In the combustion control section of the circuitry there is provided normally closed contacts 48-1 which are opened by lock-out switch heater 48, normally open con tacts 48-2 which are closed by the lock-out switch heater, contacts 62-3 which are closed on energization of control relay coil 62, and two sets of contacts operated by the flame relay, normally closed contacts 40-3- and normally open contacts 40-4.

In operation, terminals and 12 normally are energized. In response to a call for heat as signalled by control 16, blower is energized through normally closed lock-out switch contacts 48-1. As soon as air flow is produced by blower 20, switch 28 closes and energizes the primary winding 30 of transformer 32. The scanner electronics 36 are energized from the secondary winding 34 of the transformer and if the proper conditions (no flame) exist and the circuitry is operating properly, flame relay 40 remains de-energized. In this event, a circuit is completed from the secondary winding 42 of the transformer through the lock-out switch heater 48, flame relay contacts 40-1, and diode to apply a DC signal to capacitor 52. This DC signal charges capacitor 52 and is applied through resistor 54 as a bias on electrode 56 of transistor 58. This bias produces a voltage drop between electrodes 56 and 60 and establishes a bias potential on emitter 64. The timing network of resistor 66 and capacitor 68 is also energized and capacitor 68 commences to charge. When the potential on capacitor 68 exceeds the bias potential, the transistor conducts in an avalanche type characteristic, discharging capacitor 68 through electrode 60 and relay coil 62 in approximately ten milliseconds. With the energization of relay coil 62 its contact 62-1 is closed, completing a holding circuit via resistor 70.

Contacts 62-2 close, completing a low impedance circuit for the lock-out heater 48 sothat it starts a heating cycle. Contacts 62-3 also close and energize the combustion initiation components 22, 24. Fuel starts to flow to the pilot burner upon energization of component 24 and is ignited by ignition component 22. When scanner 38 senses the pilot flame, relay 40 is energized through the electronics 36 in response to the signal from scanner 38 and opens contacts 40-3 (to terminate the ignition) while closing contacts 40-4 (to permit fuel to flow to the main burner unit 26). Also on detection of flame, contacts 40-1 open, terminating the heating of the lock-out heater 48; and contacts 40-2 close, discharging capacitor 68 in :a resetting operation.

Should flame not be established within a predetermined time, as determined by the characteristics of lock-out heater 48, that heater will open contacts 48-1, de-energizing the main combustion control components 20, 22, 24, and 26; and close contacts 48-2 to energize the alarm 18.

It will be noted that the flame relay electronics 36 are powered in response to air flow produced by the blower 20 and a delay is introduced prior to initiation of the ignition cycle. Should the flame relay 40' falsely produce an indication of flame during this delay and assume an energized position, timing capacitor 68 cannot be charged, as it is shorted by contacts 40-2. Further, the charging path for that capacitor is interrupted by the opening of contacts 40-1. The system further checks the continuity of lock-out actuator 48 and the proper condition of flame relay contacts 40-1 prior to initiation of the ignition sequence. Also the system includes simple timing apparatus which delays the initiation of the ignition cycle until an adequate period 'has been provided for purging of the combustion chamber. Should the heater 48 or flame relay contacts 40-1 be open, the timing apparatus will not be energized as no DC signal is applied to capacitor 52. Throughout this pro-purge timing cycle, the flame relay electronics 36 remain energized and should erratic behavior ensue, for example, transient operation of flame relay contacts, each such operation will close contacts 40-2, discharging capacitor 68 and restarting the prepurge timing cycle.

Illustrated in FIG. 2 is a timing circuit which is an alternate to the circuit shown in FIG. 1 connected to the transformer secondary winding 42. The components which are similar to those employed in FIG. 1 are indicated by a primed reference numeral. Thus there is provided a lock-out heat-er 48' in series with flame relay contacts 40-1 connected to 18-volt terminal 46' of the transformer winding 42. A control relay contact 62-2' is connected between center tap 44' and flame relay contacts 40-1'. Diode 50 provides a DC signal for application to the timing network. That timing network includes a transistor 58' having one electrode 56' to which a bias is applied through diode and resistors 82 and 84. Filter capacitor 86 smooths the DC signal from diode 80.

The emitter electrode 64' has connected to it an RC timer circuit including resistor 66' and capacitor 68. This circuit is responsive to the charge on capacitor 52' and when the charge transferred to capacitor 68' exceeds the bias potential supplied to electrode 56', transistor 58' conducts and discharges capacitor 68' to energize the control relay coil 62' and initiate an ignition cycle. Holding contacts 62-1 close and provide a holding circuit for control relay 62.

Rather than employing contacts of a flame relay for discharging capacitor 68, diode 88 in conjunction with resistor 90 provides a discharge path for capacitors 52 and 68' should the DC charging potential via diode 50 be interrupted for any reason.

While particular embodiments of the invention have been shown and described, various modifications will be apparent to those skilled in the art. Therefore, it is not intended that the invention be limited to the disclosed embocliments or to details thereof and departures may be made therefrom within the spirit and scope of the invention as defined in the claims.

What is claimed is:

1. Burner control apparatus for use with a fuel burner installation having a combustion chamber, a fuel control for controlling the flow of fuel to said combustion chamber, and an ignition control for igniting fuel in said combustion chamber, comprising:

a control relay having a normally open fuel and ignition control switch which is closed after energization of the apparatus in response to a request for initiation of flame in the combustion chamber,

a flame sensor adapted to sense the presence of flame in the combustion chamber and having a normally closed switch which is opened upon the sensing of flame,

a safety lock-out device having a normally closed switch and a time delay switch actuator,

time delay apparatus for producing an output signal a time interval after the application of an input signal to said apparatus, said time delay apparatus including a unijunction transistor, a circuit for applying a biasing potential to said unijunction transistor in response to a request for burner operation, and a time delay network connected to the emitter electrode of said unijunction transistor for applying a potential to said emitter electrode in response to said input signal to overcome said bias potential so that said unijunction transistor produces said output signal,

and a control relay energizing circuit responsive to a request for burner operation connecting said lock-out actuator, said normally closed switch of said flame sensor and said time delay apparatus in series for application of the output signal of said time delay apparatus to energize said control relay, said control relay, upon energization, closing said normally open control relay switch to energize said fuel control and said ignition control to initiate flame in said combustion chamber.

2. The apparatus as claimed in claim 1 wherein said time delay network includes a resistance and a capacitance.

3. The apparatus as claimed in claim 2 and further including a normally open switch operated by said flame sensor, and a circuit connecting said normally open flame sensor switch across said capacitor of said time delay network.

4. Burner control apparatus for use with a fuel burner installation having a combustion chamber, an electrically energizable main fuel control valve for controlling the flow of gaseous fuel to said combustion chamber, an ignition control for igniting fuel in said combustion chamber, and a blower for forcing air through said combustion chamber in a ventilating operation, comprising:

a control relay having a normally open switch which is closed upon energization of said control relay in response to a request for initiation of flame in said combustion chamber,

a flame sensor adapted to sense the presence of flame in said combustion chamber and having a normally closed switch which is open upon the sensing of flame and a normally open switch which is closed upon the sensing of flame,

an Operating control responsive to a request for heat for applying an electrical signal to said control apparatus,

circuitry for applying said electrical signal directly to said blower,

a switch responsive to flow of air in said combustion chamber connected between said operating control and said flame sens-or and control relay for applying said electrical signal to energize said flame sensor and said control relay only after a flow of air is established in combustion chamber by said blower,

and time delay apparatus interposed between said air flow responsive switch and said control relay for delaying energization of said control relay after application of said electrical signal for a predetermined time interval, said control relay, upon energization, closing said normally open control relay switch to energize said fuel control and said ignition control to initiate flame in said combustion chamber.

5. The apparatus as claimed in claim 4 and further including a safety lock-out device having a normally closed switch and a time delay actuator, a circuit connecting said lock-out actuator in circuit between said air flow responsive switch and said control relay and said normally closed lock-out switch being connected in circuit between said operating control and said blower.

6. The apparatus as claimed in claim 5 and further including a circuit connecting said normally closed flame sensor switch in series with said lock-out actuator.

7. The apparatus as claimed in claim 4 wherein said time delay apparatus includes a unijunction transistor, and a circuit for applying a biasing potential to said unijunction transistor in response to a request for burner operation, and a time delay network connected to the emitter electrode of said unijunction transistor for applying a potential to said emitter electrode in response to said input signal to overcome said bias potential so that said unijunction transistor produces said output signal.

8. The apparatus as claimed in claim 7 wherein said time delay network includes a resistance and a capacitance.

9. The apparatus as claimed in claim 8 and further including a normally open switch operated by said flame sensor, and a circuit connecting said normally open flame sensor switch across said capacitance of said time delay network.

10. The apparatus as claimed in claim 9 and further including a circuit responsive to said output signal of said time delay apparatus for bypassing said time delay apparatus and maintaining said control relay energized.

11. The apparatus as claimed in claim 10 wherein said bypass circuit includes a second normally open switch operated by said control relay.

12. The apparatus as claimed in claim 11 wherein said energizing circuit is connected across the secondary winding of a transformer and wherein said control relay further includes a second normally open switch, and further including a circuit connecting said second normally open control relay switch between an intermediate voltage tap of said secondary winding and a high voltage terminal of said secondary winding via said lock-out actuator and the normally closed switch of said flame sensor to provide a timing circuit for terminating the ignition cycle if flame is not established in said combustion chamber.

13. Burner control apparatus for use with a fuel burner installation having a combustion chamber, and a fuel control for controlling the flow of fuel to said combustion chamber, comprising:

a control relay having a normally open switch which is closed upon energization of the apparatus in response to a request for initiation of flame in the combustion chamber,

a flame sensor adapted to sense the presence of flame in the combustion chamber, said flame sensor including a switch which is operated upon the sensing of flame,

time delay apparatus responsive to a request for burner operation for producing an output signal a time interval after the application of an input signal to said apparatus, said time delay apparatus including a capacitor which is charged in response to said input signal and control for translating a predetermined charge on said capacitor as said output signal,

a circuit connecting said flame sensor switch in circuit with the input to said time delay apparatus for discharging said capacitor upon operation of said flame sensing switch prior to product-ion of said output signal,

and a control relay energizing circuit for applying the output signal of said time delay apparatus to energize said control relay,

said control relay, upon energization, closing said normally open control relay switch to energize said fuel control to initiate a combustion condition in said combustion chamber.

14. Burner control apparatus for use with a fuel burner installation having a combustion chamber, a fuel control for controlling the flow of fuel to said combustion chamber, and an ignition control for igniting fuel in said combustion chamber, comprising:

a control relay having a normally open fuel and ignition control switch which is closed after energization of the apparatus in response to a request for initiation of flame in the combustion chamber,

a flame sensor adapted to sense the presence of flame in the combustion chamber and having a normally closed switch which is opened upon the sensing of flame,

a safety lock-out device having a normally closed switch and a time delay switch actuator,

time delay apparatus for producing an output signal a time interval after the application of an input signal to said apparatus,

a control relay energizing circuit responsive to a request for burner operation connecting said lock-out actuator, said normally closed switch of said flame sensor and said time delay apparatus in series for application of the output signal of said time delay apparatus to energize said control relay, said control relay, upon energization, closing said normally open control relay switch to energize said fuel control and said ignition control to initiate flame in said combustion chamber, and

a circuit responsive to said output signal of said time delay apparatus for bypassing said time delay apparatus and maintaining said control relay energized.

15. The apparatus as claimed in claim 14 wherein said bypass circuit includes a second normally open switch operated by said control relay.

16. Burner control apparatus for use with a fuel burner installation having a combustion chamber, a fuel control for controlling the flow of fuel to said combustion chamber, and an ignition control for igniting fuel in said combustion chamber, comprising:

a control relay having a first normally open fuel and ignition control switch is closed after energization of the apparatus in response to a request for initiation of flame in the combustion chamber, and a second normally open switch,

a flame sensor adapted to sense the presence of flame in the combustion chamber and having a normally closed switch which is opened upon the sensing of flame,

a safety lock-out device having a normally closed switch and a time delay switch actuator,

time delay apparatus for producing an output signal a time interval after the application of an input signal to said apparatus,

a control relay energizing circuit responsive to a request for burner operation connecting said lock-out actuator, said normally closed switch of said flame sensor and said time delay apparatus in series for application of the output signal of said time delay apparatus to energize said control relay, said control relay, upon energization, closing said first normally open control relay switch to energize said fuel control and said ignition control to initiate flame in said combustion chamber, said energizing circuit being connected across the secondary winding of a transformer, said secondary winding having a high voltage terminal and an intermediate voltage tap,

and a circuit connecting said second normally open control relay switch between said intermediate voltage tap and said high voltage terminal via said lockout actuator and the normally closed switch of said flame sensor to provide a timing circuit for terminating the ignition cycle if flame is not established in said combustion chamber.

17. Burner control apparatus for use with a fuel burner installation having a combustion chamber, a fuel control for controlling the flow of fuel to said combustion chamher, and an ignition control for igniting fuel in said combustion chamber, comprising:

a control relay having a normally open fuel and ignition control switch which is closed after energization of the apparatus in response to a request for initiation of flame in the combustion chamber,

a flame sensor adapted to sense the presence of flame in the combustion chamber and having a normally closed switch which is opened upon the sensing of flame,

a safety lock-out device having a normally closed switch and a time delay switch actuator,

time delay apparatus for producing an output signal a time interval after the application of an input signal to said apparatus, said time delay apparatus including a network including resistor and a capacitor,

a control relay energizing circuit responsive to a request for burner operation connecting said lock-out actuator, said normally closed switch of said flame sensor and said time delay apparatus in series for application of the output signal of said time delay apparatus to energize said control relay, said control relay, upon energization, closing said normally open control relay switch to energize said fuel control and said ignition control to initiate flame in said combustion chamber,

and a circuit arrangement for discharging said capacitor in the event said flame sensor produces a flame indication before said control relay is energized.

18. The apparatus as claimed in claim 17 wherein said circuit includes a normally open switch of said flame sensor connected across said capacitor.

19. The apparatus as claimed in claim 17 wherein said circuit includes an asymmetrically conductive device connected across said resistor,

20. The apparatus as claimed in claim 17 wherein said installation further includes a blower for forcing air through said combustion chamber, and said control apparatus includes a circuit connecting said blower for response directly to energization of said apparatus upon occurrence of a call for heat.

21. The apparatus as claimed in claim 20 and further including a switch responsive to air flow in said combustion chamber connected to energize said flame sensor and said control relay energizing circuit when air flow is produced in said combustion chamber in response to a call for heat.

22. Burner control apparatus for use with a fuel burner installation having a combustion chamber, a fuel control for controlling the flow of fuel to said combustion chamber, and an ignition control for igniting fuel in said combustion chamber, comprising:

a control relay having a normally open fuel and ignition control switch which is closed after energization of the apparatus in response to a request for initiation of flame in the combustion chamber,

a flame sensor adapted to sense the presence of flame in the combustion chamber and having a normally closed switch which is opened upon the sensing of flame,

a safety lock-out device having a normally closed switch and a time delay switch actuator,

time delay apparatus for producing an output signal a time interval after the application of a flame request signal to said apparatus, said time delay apparatus includes a transistor, a circuit for applying a biasing potential to said transistor, and a time delay network connected to said transistor for applying a potential to said transistor in response to said input signal to overcome said bias potential so that said transistor produces said output signal,

and a control relay energizing circuit responsive to a request for burner operation connecting said lock-out actuator, said normally closed switch of said flame sensor and said time delay apparatus in series for application of the output signal of said time delay apparatus to energize said control relay, said control relay, upon energization, closing said normally open control relay switch to energize said fuel control and said ignition control to initiate flame in said combustion chamber.

References Cited JAMES W. WESTHAVER, Primary Examiner. 

